A simple apparatus for tensile testing of rock

Abstract

Measuring tensile strength of a quasi-brittle material such as rock is a challenging task. Indirect tensile testing methods such as the Brazilian and flexural tests rely on the assumption of linear elastic behavior, which is not valid close to the peak stress. The direct tensile testing method is independent of the constitutive response of the material and should provide more realistic data. Nevertheless, the test set up in direct tensile testing is time consuming and the results can depend on the applied boundary conditions. In this work, a new apparatus is introduced that can measure tensile strength of quasi-brittle materials and provide information regarding the crack opening behavior. The apparatus, which is an aluminum or steel beam with a cut-out and central notch, acts as both the loading fixture and load cell. The specimen is attached to the central part of the apparatus using an epoxy adhesive . Strain gages mounted on the two sides of the apparatus provide the necessary information about the tensile behavior of the specimen. The device is also capable of detecting and quantifying the intensity of asymmetric failure (crack growth) in the specimen, as identified by digital image correlation . The apparatus, its calibration, and some tests results are presented and discussed. • A new apparatus for tensile testing of rock is introduced. • Uniaxial tensile strength and critical crack opening of Charcoal granite are measured. • Comparison is made between the data collected using the new and conventional uniaxial tensile testing devices. • Digital image correlation is used to study the failure process.